I think they should write a small warning on the bottom in red text, so then the mages and wizards can get a heads-up for what might happen. That gives the clean-up crew less work to do, since they'll probably have to trap those worms and keep them in place, do some magical things, and chant/perform another spell to un-summon them. If they don't get eaten first, too

That's okay. I can wait (or rather, a few hundred thousand children can wait for this card game, or a few hundred thousand DnD addicts). I myself have no love for card games any more, though that can change.